Injection  valve,  method  for  its  production,  and  apparatus  for  performing  the  method

ABSTRACT

The invention relates to a method for producing an injection valve for liquids, preferably an injection valve for injecting fuel into a combustion chamber of an internal combustion engine. The injection valve has a valve body, with a valve seat which is formed therein, and a valve needle which interacts with the valve seat in order to open and close at least one injection opening. The injection valve is produced by means of the following method steps: producing the valve body from steel, hardening the valve body, annealing a partial region of the valve body at an annealing temperature. The device for carrying out the method according to the invention has an inductive annealing generator which generates a suitable alternating current for operating a coil, in the magnetic field of which coil the valve body can be heated for annealing.

PRIOR ART

The invention relates to a method for producing an injection valve ofthe kind known for instance from European Patent EP 233 190 B1.Injection valves of the kind preferably used for injecting fuel at highpressure into a combustion chamber of an internal combustion engine areproduced in a plurality of work steps. In a first work step, the actualvalve body is shaped from steel, the steel being still unhardened andthus easily machined. After the production of the outer and inner shapeof the injection valve, the valve is subjected to a hardening process,in which the injection valve is severely heated and then quenched. Foreliminating stresses that are caused by the uneven cooling down of thevalve body, the hardening is followed by a heat treatment of the valvebody, that is, a first annealing, in which the valve body is held for acertain period of time at an elevated temperature below the hardeningtemperature, until the stresses that have built up are adequatelyreduced. The valve body can be heated by various methods, for instancein an oil bath or by inductive heating, which is known for instance fromGerman published patent application DE-OS 1 292 696.

Injection valves of the kind used for injecting fuel at high pressureinto combustion chambers of internal combustion engines operate in thefollowing way: A valve needle is disposed longitudinally displaceably inthe valve body and cooperates with a valve seat for opening and closingat least one injection opening. By a longitudinal motion of the valveneedle, the injection is initiated and interrupted, so that a preciseinjection of fuel at high pressure into the combustion chamber isattained. This puts a severe strain on the valve needle in the regionwhere it is guided and on the valve seat, but wear is lessened by theaforementioned hardening of the valve body.

In modern valve bodies, upon their first use once engine operation hasbegun, a partial transformation of the microstructure of the materialtakes place, which leads to a change in shape in the nozzle seat at theplace where the valve needle is seated on the nozzle. This change inshape causes a change in the quantity injected, so that the injectionvalve no longer operates as it did when it was new, which is especiallydisadvantageous in common rail injection systems.

It is not possible to optimize the valve body in every respect: Longerannealing at higher temperatures does increase the toughness of thesteel but also lessens its hardness, so that the wear in the region ofthe valve seat and of the needle guidance becomes greater. On the otherhand, if the annealing is done at lower temperatures or for a shortertime, then the valve body remains relatively brittle, and cracks canoccur, particularly in the region of the valve seat.

Advantages of the Invention

The method according to the invention for producing an injection valvehas the advantage that the transformation in the microstructure thatoccurs in injection valves is anticipated by two successively performedheat treatments. These heat treatments for reducing the internalstresses (annealing) have the effect that the change in quantityassociated with the microstructural transformation does not occur inoperation and hence afterward, and thus the injection properties of theinjection valve remain constant over its entire service life. To thatend, after the production and hardening, the entire valve body isannealed at a temperature T₁. Next, a second annealing process follows,in which only a partial region of the valve body is heated, this partialregion including the valve seat, and this is done at an annealingtemperature T₂ that is higher than the first annealing temperature T₁.As a result, the hardness of the valve body, in the region where thevalve needle is guided, is preserved to a sufficient extent, and wear isthus correspondingly low. On the other hand, the valve seat isintentionally made tougher by the increased annealing temperature, sothat brittle failure in this region is avoided. The temperature of thefirst annealing process T₁ is below the second annealing temperature T₂and amounts to from 150 to 240° C., preferably being approximately 180°C.

In a first advantageous refinement of the method, the valve body isfilled with a fluid during the second annealing, and this fluid is underpressure, preferably being at the maximum incident pressure at which theinjection valve is to be operated. As a result, especially whenever thevalve needle is likewise urged by a force in the direction of the valveseat, conditions are created of the kind that occur also upon first useof the injection valve once engine operation has begun. If the secondannealing process is performed under these conditions, theaforementioned microstructural transformation in the steel of the valvebody occurs and hence there is compensation between the valve needle andthe valve seat, so that the process that not daily takes place uponfirst operation of the injection valve is already anticipated here. Thethus-altered injection behavior of the injection valve can be taken intoaccount by suitable programming of the engine control unit, so that afurther change in the injection behavior after installation in theengine need not be expected.

In a further advantageous feature, the second annealing takes place byinductive heating of the valve body. By a suitable design of the coilthat generates the corresponding alternating magnetic field, the valvebody can be heated very purposefully in the desired region to theappropriate temperature. Preferably, the valve body is heated to atemperature of the kind that also occurs during engine operation in thevalve body as a result of the heat in the combustion chamber. A secondannealing temperature of 250 to 400° C. has proved especiallyadvantageous, given a first annealing temperature of 160 to 240° C.

DRAWINGS

In the drawings, objects that have been produced by the method of theinvention as well as apparatuses for performing the invention are shown.

FIG. 1 shows an injection valve, which is of the kind used for injectingfluids into combustion chambers of internal combustion engines and whichcan be produced by the method of the invention.

FIGS. 2, 3 and 4 each show apparatuses for performing the method of theinvention.

DESCRIPTION

FIG. 1 shows a longitudinal section through an injection valve which canbe produced by the method of the invention. The injection valve, whichin the egg in an internal combustion engine is connected to an injectorbody, not shown in FIG. 1, has a valve body 1 in which a bore 3 is made.The bore 3 is defined, on its end toward the combustion chamber, by avalve seat 6, which has an essentially conical shape and opens into ablind bore 9. A plurality of injection openings 7, through which thefuel is ejected in operation of the injection valve, extend from theblind bore 9. A valve needle 5 embodied in pistonlike shape is disposedlongitudinally displaceably in the bore 3, and on its end remote fromthe valve seat it has a guide portion 15, with which the valve needle isguided in fluid-tight fashion in the bore 3. As a result, a pressurechamber 19, which surrounds the valve needle 5 between the guide portion15 and the valve seat 6, is sealed off by the slight guidance play inthe region of the guide portion 15.

In its end toward the valve seat the valve needle 5 has a sealing face11, which is likewise embodied essentially conically and with which thevalve needle 5 cooperates with the valve seat 6. The valve needle 5cooperates with the valve seat 6 in such a way that when the sealingface 11 becomes seated on the valve seat 6, the injection openings 7 aresealed off from the pressure chamber 19, while when the valve needle 5is lifted from the valve seat 6, the blind bore 9 and thus the injectionopenings 7 communicate with the pressure chamber 19. In turn, thepressure chamber 19 then fills with fuel at high pressure via an inletbore 25 extending in the valve body 1.

The longitudinal motion of the valve needle 5 inside the bore 3 iscontrolled by the ratio of a closing force, which acts on the end of thevalve needle 5 remote from the valve seat, and the hydraulic force,which is exerted on parts of the sealing face 11 and on a pressureshoulder 13 by the pressure in the pressure chamber. Since theindividual injections, especially when the injection valve is used inhigh-speed self-igniting internal combustion engines, occur in a veryshort time and in very rapid succession, the valve needle 5 must bemoved with strong force and at a high speed. This makes stringentmechanical demands of the valve needle 5 itself and of the valve body 1,especially in the region of the valve seat 6.

In order to construct an injection valve to meet these demands, it isproduced according to the invention by the following method: First, thevalve body is produced from steel; the steel is not yet hardened and hasgood machinability, for instance by forging or by material-removingprocesses. Once the outer shape and the bore, including the valve seat,have been produced, the valve body is hardened, preferablycase-hardened, in order to attain suitable hardness and wear resistance.Since in the hardening process strong intrinsic stresses occur insidethe valve body, and furthermore after the hardening the valve body isstill quite brittle, a fracture in the region of the valve seat 6 wouldeasily occur during operation. To prevent this, the hardening process isfollowed by a heat treatment, in which the entire valve body 1 is heatedto a temperature T₁, which preferably amounts to from 150 to 240° C.,and is held for a period of time at that temperature. By means of thisheat treatment, intrinsic stresses inside the valve body diminish, andthe toughness of the material increases.

In modern valve bodies, on first use of the entire installed injector inthe guide portion, a partial transformation of the microstructure of thematerial takes place in the region of the valve seat 6. This leads tochanges in shape in the valve seat 6 and thus to a change in theinjected quantity, which is disadvantageous, especially in common railinjection systems. This is explained by the fact that once operation hasbegun, the tip of the injection valve, which is toward the combustionchamber and is where the valve seat 6 is located, is subjected both tothe heat of the combustion chamber and to strong hydraulic andmechanical forces by the valve needle 5 and by the high fuel pressurepresent in the pressure chamber 19, which can amount to up to 2000 bar.To anticipate this transformation in the microstructure, in theproduction method of the invention a second annealing process of thevalve body 1 is provided, in the region that is subjected to theincreased engine temperature, which in operation can amount to up to300° C. This region is the end region of the valve body 1 where thevalve seat 6 is also located. Accordingly, after the hardening and firstannealing, the valve body 1 is subjected to a second annealing processat a temperature T₂, which essentially corresponds to the temperaturethat occurs in the injection valve once engine operation has begun.

In principle, heating the valve body 1 can be done in various ways: Itcan be done conventionally, for instance in an oil bath, by dipping thevalve body 1 to the desired height into the hot oil. However, heating bymeans of an induction process has proved especially advantageous, inwhich the valve body 1 is placed in a coil to which a suitablealternating current is applied. The magnetic field occurring inside thecoil induces eddy currents in the valve body, which assure heating andthus increase the temperature of the valve body purposefully in theregion that is subjected to the magnetic field. This inductive annealingcan happen very quickly, and in the case of a valve body it takes only afew seconds. FIG. 2 shows a suitable arrangement for this, whichincludes an inductive annealing generator 35 that generates a suitablealternating current and conducts it through a coil 37. Inside the coil,the aforementioned alternating magnetic field occurs, and the coil 37 isdimensioned such that the valve body 1 can be disposed with its endtoward the valve seat inside the coil 37. In the embodiment shown inFIG. 2, the valve body 1 is connected to an injector body 2, so that allin all, a fuel injector is formed that can be installed in an internalcombustion engine in order there to inject fuel into a combustionchamber.

The balance between the valve seat 6 and the valve needle 5 in theinductive annealing is especially effective whenever the injector issubjected to the conditions that also occur in operation in the engine,that is, to the corresponding forces and the requisite fuel pressure.For that purpose, in the annealing the injector can fill with fuel athigh pressure, but without an injection taking place. To that end, via ahigh-pressure line 32, the injector body 2 is made to communicate with ahigh-pressure pump 30, which makes a suitable fuel pressure availableand puts the injector body 2, precisely like the valve body 1, underhigh fuel pressure. Under these conditions, the valve needle 5 is alsopressed with strong force against the valve seat 6, so that acorresponding balance between the valve seat 6 and the valve needle 5 orsealing face 11 occurs in the inductive annealing. This annealingprocess can be done with the injector in its fully installed state, orin other words as the final process step in the production of the entirefuel injector.

FIG. 3 shows an apparatus for inductive annealing which is practicallyequivalent to what is shown in FIG. 2, but here only the injectionvalve, after its manufacture, is inductively annealed without beingconnected to an injector body. Once again, fuel is introduced into thevalve body 1 at high pressure via the high-pressure pump 30 and thehigh-pressure line 32; the valve needle is either stopped or is pressedby a different device against the valve seat 6 with a suitable force.

A further alternative method and its apparatus are shown in FIG. 4.Here, the valve body 1 is subjected to an inductive annealing processthat ensues immediately after the heat treatment of the valve body 1.This process step can indeed be integrated quite economically into theoverall manufacture of the valve body 1, but that has the disadvantagethat grinding processes still follow, and no balance between the valveneedle 5 and the valve seat 6 is established.

By the inductive annealing of the end region of the valve body 1, onlythat region is increased in its toughness, and because of the skineffect, that is, the fact that the eddy currents are generated primarilyat the surface of the metal valve body 1, only the surface of the valvebody 1 is made tougher, while the remainder of the valve body 1 is givena greater hardness. Since the annealing process does not affect theregion of the bore 3 remote from the valve seat, the good wearproperties of the hardened valve body 1 in the region of the guideportion 15 of the valve needle 5 are unimpaired.

The first annealing of the valve body 1 is typically done at atemperature T₁ of from 150 to 240° C., preferably at approximately 180°C. The temperature during the second annealing in the end region of thevalve body preferably amounts to from 250 to 400° C., and a temperatureof from 270 to 300° C. is especially advantageous. The applied fuelpressure preferably corresponds precisely to the maximum pressure thatoccurs in operation of the injection valve in the engine, but it mayalso be lower. This means a fuel pressure that at maximum isapproximately 1600 to 2000 bar.

1-14. (canceled)
 15. A method for producing an injection valve forfluids, preferably an injection valve for injecting fuel into acombustion chamber of an internal combustion engine, which has a valvebody with a valve seat embodied therein and a valve needle thatcooperates with the valve seat for opening and closing at least oneinjection opening, comprising the following method steps: producing thevalve body from steel; hardening the valve body; first annealing of theentire valve body at a first annealing temperature; second annealing ofa partial region of the valve body at a second annealing temperature,wherein the first annealing temperature being lower than the secondannealing temperature.
 16. The method as defined by claim 15, whereinthe partial region includes the valve seat.
 17. The method as defined byclaim 15, wherein the valve body is filled with a fluid during theannealing.
 18. The method as defined by claim 17, wherein the fluid isunder pressure.
 19. The method as defined by claim 18, wherein thepressure corresponds to the maximum incident pressure at which theinjection valve ejects the fluid in operation.
 20. The method as definedby claim 17, wherein the valve needle is pressed against the valve seatwith a force during the annealing.
 21. The method as defined by claim18, wherein the valve needle is pressed against the valve seat with aforce during the annealing.
 22. The method as defined by claim 19,wherein the valve needle is pressed against the valve seat with a forceduring the annealing.
 23. The method as defined by claim 20, wherein thevalve needle is pressed against the valve seat with a maximum force thatoccurs in operation of the injection valve.
 24. The method as defined byclaim 21, wherein the valve needle is pressed against the valve seatwith a maximum force that occurs in operation of the injection valve.25. The method as defined by claim 22, wherein the valve needle ispressed against the valve seat with a maximum force that occurs inoperation of the injection valve.
 26. The method as defined by claim 15,wherein the first annealing and/or the second annealing is performed byinductive heating of the valve body.
 27. The method as defined by claim25, wherein the first annealing and/or the second annealing is performedby inductive heating of the valve body.
 28. The method as defined byclaim 15, wherein the injection valve is an injection valve of the kindfor injecting fuel at high pressure into a combustion chamber of aninternal combustion engine, and in the second annealing, the part of thevalve body is heated that is also heated the most by heat in thecombustion chamber during the operation of the engine.
 29. The method asdefined by claim 27, wherein the injection valve is an injection valveof the kind for injecting fuel at high pressure into a combustionchamber of an internal combustion engine, and in the second annealing,the part of the valve body is heated that is also heated the most byheat in the combustion chamber during the operation of the engine. 30.The method as defined by claim 15, wherein the second annealingtemperature amounts to 250 to 400° C.
 31. The method as defined by claim15, wherein the first annealing temperature amounts to 160 to 240° C.32. An injection valve for injecting fuel into a combustion chamber ofan internal combustion engine, characterized in that it is produced inaccordance with the method according to claim
 15. 33. An apparatus forperforming the method as defined by claim 15, comprising an inductiveannealing generator and a coil electrically connected to the inductiveannealing generator, wherein the valve body can be disposed in such away inside a magnetic field generated by the coil that upon applicationof a suitable alternating voltage to the coil, only a part of the valvebody is heated by induced eddy currents from the inductive annealinggenerator.
 34. The apparatus as defined by claim 33, wherein the coil isshaped such that an end of the valve body that is toward the combustionchamber can be disposed inside the coil in such a way that only that endis heated by the induced eddy currents.